GCC Rust Weekly Status Report 29

Thanks again to Open Source Security, inc and Embecosm for their ongoing support for this project.

Milestone Progress

This week my focus was on the linux plumbers conference so I was not able to complete any tickets for the current milestone, though I have made some good progress in investigating closures in C++ and GO to gain an understanding of how they are implemented in GCC. I expect to see progress this week.

Monthly Community Call

We will be having our 7th community call on the first Friday of the month:

Date and Time 1st October 2021 at: 09h00 UTC
Agenda: https://hackmd.io/FBNWz8LyQk2vOaEsQtex1g please feel free to add agenda items you wish to see discussed.
Jitsi: https://meet.jit.si/259057065581073

Linux Plumbers 2021 Talk

Please find the video of my talk here:

The slides are also available here: https://linuxplumbersconf.org/event/11/contributions/911/

Closure investigation

Since rust closures are similar to C++ in that they can be moved, I thought it makes sense to investigate how they work there first, for example, a C++ closure such as:

int test() {
    int capture = 456;
    auto a = [&](int a) -> int {
        return a + capture;
    };
    return a(123);
}

Breaks down into the following:

int test ()
{
  int D.2400;
  int capture;
  struct ._anon_0 a;
  typedef struct ._anon_0 ._anon_0;

  try
    {
      capture = 456;
      a.__capture = &capture;
      D.2400 = test()::<lambda(int)>::operator() (&a, 123);
      return D.2400;
    }
  finally
    {
      capture = {CLOBBER};
      a = {CLOBBER};
    }
}

int test()::<lambda(int)>::operator() (const struct ._anon_0 * const __closure, int a)
{
  int D.2403;
  int & capture [value-expr: __closure->__capture];

  _1 = __closure->__capture;
  _2 = *_1;
  D.2403 = a + _2;
  return D.2403;
}

This shows that you can break down a closure into a structure to hold onto captured data by reference. Then the actual lambda itself the variables which it captures are a type of “static chain” variable as you can see above. Where the capture variable was captured but refers to the parameter of the closure object’s reference.

Detailed changelog

Fix GCC Bootstrap builds

Thanks to our whole community who have worked on this to eliminate all the compiler warnings which allows us to perform a full GCC bootstrap build. See our tracking issue for all related fixes to get this working: https://github.com/Rust-GCC/gccrs/issues/336

We will need to add some automation to track compiler warnings in the CI build to catch regressions for bootstrap builds in PR’s.

Merge from upstream GCC

Thanks to Thomas Schwinge we have merged with the latest upstream GCC. The last merge was completed in and around six months ago, this means we get all the relevant updates for DCO contributions and ensure our front-end code is not drifting to become unmergeable. See below before what the –version looked like:

gccrs (GCC) 11.0.1 20210325 (experimental)
Copyright © 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

After

gccrs (GCC) 12.0.0 20210917 (experimental)
Copyright © 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Fix bug with out of range characters

Mark Wielaard identified a bug with our lexer which was incorrectly flagging byte with their high-bit set, this was due to a bad unsigned vs signed check.

bytecharstring.rs:3:14: error: ‘byte char’ ‘�’ out of range
    3 |   let _bc = b'\x80';
      |              ^
bytecharstring.rs:4:14: error: character ‘�’ in byte string out of range
    4 |   let _bs = b"foo\x80bar";
      |              ^

Completed Activities

Fix bootstrap build PR689 PR690 PR688
Fix bug in lexer for out of range characters PR687

Contributors this week

Excluding merges, 3 authors have pushed 6 commits to master and 6 commits to all branches. On master, 11,609 files have changed and there have been 673,665 additions and 375,942 deletions.

Overall Task Status

Category	Last Week	This Week	Delta
TODO	90	90	–
In Progress	6	7	+1
Completed	197	198	+1

GitHub Issues

Test Cases

Category	Last Week	This Week	Delta
Passing	4425	4428	+3
XFAIL	21	21	–

make check-rust

Bugs

Category	Last Week	This Week	Delta
TODO	22	21	-1
In Progress	3	3	–
Completed	67	68	+1

GitHub Bugs

Milestones Progress

Milestone	Last Week	This Week	Delta	Start Date	Completion Date	Target
Data Structures 1 – Core	100%	100%	–	30th Nov 2020	27th Jan 2021	29th Jan 2021
Control Flow 1 – Core	100%	100%	–	28th Jan 2021	10th Feb 2021	26th Feb 2021
Data Structures 2 – Generics	100%	100%	–	11th Feb 2021	14th May 2021	28th May 2021
Data Structures 3 – Traits	100%	100%	–	20th May 2021	17th Sept 2021	27th Aug 2021
Control Flow 2 – Pattern Matching	0%	0%	–	20th Sept 2021	–	29th Nov 2021
Imports and Visibility	0%	0%	–	–	–	TBD
Macros and cfg expansion	0%	0%	–	–	–	TBD
Const Generics	0%	0%	–	–	–	TBD
Intrinsics	0%	0%	–	–	–	TBD

GitHub Milestones

Planned Activities

Continue work on closure types
Fix docker automation issues
Add compiler warning automation for GHA